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Old 7th February 2008, 02:26 AM   #1
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Default Another big horn dream... comments and concerns?

Click the image to open in full size.

This is a pic I drew up a few days ago and it's just so pretty I can't stop thinking about it. It's definitely not on the to do list, but it would be easier to make than floor to ceiling stacks of labhorns, so I might do it one day. A side benefit is that it turns the whole front wall into a poly cylindrical diffusor. I would expect to design this to cover somewhere around 10 - 40 hz or so.

The red outline is a massive floor to ceiling sealed box. The walls and the box form a dual waveguide with a rapid expansion that grows to the cross sectional area of the room at the mouth. So technically it's not really a horn. This would use as many highish vas 15 or 18 inch woofers (like the new tempestx) as it takes to maintain a decent system q and provide adequate spl, hopefully with loads of extra headroom.

I would use this in a small room so the dimensions and amount of drivers don't get out of hand. The walls of the room would need to be made of concrete or metal, in which case there should be lots of room gain (and lots of room treatments). A 10x7.5 foot front wall would amount to a mouth size of 75 square feet.

1. How do you model something like this? Since the mouth is the entire cross sectional area of the room, it's not 1/8th space, more like 1/16 or maybe even 1/32 space, I would think. ???

2. Should there be a front chamber? A front chamber would probably net some more spl potential, especially down low, but is that a good trade when spl levels should be more than enough anyway?

3. Would it be better to just do floor to ceiling stacks of labhorns in the front corners?

It's pointless to even try to model it without knowing it's context in relation to the room, so I haven't even tried yet.
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Old 7th February 2008, 11:22 AM   #2
MaVo is offline MaVo  Germany
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1) easy approach:
one approach may be to model only the horn to the mouth and take everything that follows due to the room being smaller than 1/8 space as added bonus. another one may be to use hornresp and simulate part of the room as a part of the horn. both together could lead at least lead to a rough impression of what the room will do to the sound.

room influence:
i would think that the room wont act as a part of the horn, since its area doesnt change anymore, after your horn extension is finished. it will act more likely as an more or less sealed chamber, providing room gain below its fundamental and resonances above.

best approach:
best results will be achieved by using Akabak and modelling the whole system of horn and room as a whole. but i was too lazy to script something like that until now. maybe if i finally get to build a real subwoofer some day.

2) can only be answered by simulating the horn

3) labhorns are very efficient above 30hz, below they act more and more as a sealed box. if you want this, go with it. but you could build a horn with a behaviour, that matches your needs better, as the compromises of the lab were geared towards prosound and not home installation. for example a lower cutoff could be achieved.
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Old 7th February 2008, 12:06 PM   #3
tinitus is offline tinitus  Europe
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Looks like a Lansing model just bigger, cant remember the name

Appears to be a good project with huge mouth area, so it doesnt matter that I think the mouth will only be reduced by floor and sidewalls, which means 1/4...unless you plan to make it all the way from floor to ceiling

But I suppose you will need a smaller chamber at the back of driver(s), thus it will leave you with a lot of wasted space in the middle...maybe you could just use some hinged "wings" or "loose" baffles to support mouth transistion

As suggested the Labhorn might be better fore you, and the easy way out...maybe with additional wings
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Old 7th February 2008, 03:14 PM   #4
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Thanks guys.

Quote:
Looks like a Lansing model just bigger, cant remember the name
I haven't seen anything like this before but there's nothing new under the sun (except tapped horns) so this shape has probably been seen in a few different designs in decades past.

Quote:
unless you plan to make it all the way from floor to ceiling
Floor to ceiling is the plan, making it any shorter would drastically reduce it's performance, I think.

Quote:
But I suppose you will need a smaller chamber at the back of driver(s),
Since it's not to scale and there's no way to accurately guess without at least trying to model it, off the top of my head I'm going to say the sealed box part contains about 100 cubic feet of air (based on a small room size with a front wall 7.5x10 feet and lots of internal bracing). Highish vas woofers like to be in a big sealed box. The tempestx looks like it needs about 13.5 cubic feet of sealed box to hit a .7 q. This amounts to about 8 drivers, which is actually pretty reasonable when you consider what goes into dual floor to ceiling stacks of labhorns, so I don't think I need to make the box smaller. Besides, making it significantly smaller would mess up the shape of the waveguide.

Quote:
one approach may be to model only the horn to the mouth and take everything that follows due to the room being smaller than 1/8 space as added bonus. another one may be to use hornresp and simulate part of the room as a part of the horn.
The first idea may lead to a whole lot of eq to flatten out the end result, since it's only a guess. WRT hornresp... I would think you are right about akabak being the best tool for this job, since the room is a big part of this equation, but I have no idea how to use it. Even if I did, I would not know if I was doing an accurate model, since I would have no idea what results to expect.

Quote:
3) labhorns are very efficient above 30hz, below they act more and more as a sealed box. if you want this, go with it. but you could build a horn with a behaviour, that matches your needs better, as the compromises of the lab were geared towards prosound and not home installation. for example a lower cutoff could be achieved.
I know a bit about the labhorn, and there are other horns out there with a 30 hz low end, not much below that. There's two ways to get lower response afaik, either make a larger single horn or stack the smaller horns to sum the mouths. A floor to ceiling stack of labhorns or similar could probably easily be flat to 20 hz, which is higher than I was hoping for and probably provide 30 db of extra unused dynamic potential. I was hoping to be able to trade that type of response for (much) lower tuning at the cost of peak spl with a single large "horn", hopefully with little or no eq.
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Old 7th February 2008, 03:41 PM   #5
MaVo is offline MaVo  Germany
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Flat to 20hz may be a bit optimistic, since only the mouth area grows and the horn length stays the same (ignoring the fact, that the bigger mouth may lead to a slightly longer "virtual" horn). this should rather flatten the response. But since a stack of maybe 4 labs will be 8 12inch drivers, those alone will provide deep bass, even without horn loading.

Make a search over at http://www.prosoundweb.com/forums/ since Tom has covered this subject there allready. i think search subject "10hz" could be usefull.
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Old 7th February 2008, 04:00 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
Mavo's right. The expansion rate (flare) in the Labhorn is designed to perform down to 27Hz.
If the full mouth area matches the space loading this is achieved.
Using fewer boxes than required by the loading is equivalent to truncating the horn and leads to ripples in the response.

Increasing the area does not improve the horn. It does provide better coupling for the sealed bass unit that result below the effective horn frequency. I suspect there will be a step in the frequency response as the horn hands over to sealed box.
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Old 7th February 2008, 05:00 PM   #7
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Quote:
Originally posted by tinitus
Looks like a Lansing model just bigger, cant remember the name

Paragon?

Click the image to open in full size.
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Old 7th February 2008, 05:08 PM   #8
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Is the brown dot-thingie on the drawing the victim ?????

Regards

Charles
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Old 7th February 2008, 05:47 PM   #9
tinitus is offline tinitus  Europe
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Old 7th February 2008, 06:29 PM   #10
tinitus is offline tinitus  Europe
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Not an expert but common sense tells me that waht you want is impossible...your horn would need to be much bigger, a big mouth is not all there is to it

Why not build something with multiple sub drivers in BIG fronthorn, floor to ceiling and a bit of EQ
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